1. Field of the Invention
The present invention relates to an apparatus for and a method of erasing a residual radiation image from a stimulable phosphor panel by applying erasing light to the stimulable phosphor panel after a radiation image has been read from the stimulable phosphor panel by applying stimulating light to the stimulable phosphor panel.
2. Description of the Related Art
There has heretofore been known a stimulable phosphor which, when exposed to radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet radiation, or the like), stores part of the energy of the radiation, and, when subsequently exposed to stimulating rays such as visible light, emits light in proportion to the stored energy of the radiation.
A radiation image information recording and reproducing system, which has been developed in the art, temporarily records a radiation image of a subject such as a human body on a stimulable phosphor panel having a stimulable phosphor layer. Thereafter, the radiation image information recording and reproducing system applies stimulating light such as a laser beam or the like to the stimulable phosphor panel to emit light representative of the recorded radiation image, and then outputs the radiation image as a visible image on a recording medium such as a photosensitive medium or the like or a display unit such as a CRT or the like, based on an image signal that is generated by photoelectrically reading the light emitted from the stimulable phosphor panel. After the radiation image has been read from the stimulable phosphor panel, the stimulable phosphor panel is irradiated with erasing light to erase any remaining radiation image therefrom, and then used again for recording a radiation image thereon.
If erasing light exclusive of ultraviolet radiation is used to erase the remaining radiation image from the stimulable phosphor panel, then electrons trapped in a deep layer where they cannot be removed by visible erasing light tend to remain unremoved. Conversely, if erasing light including much ultraviolet radiation is used, then though those trapped electrons can be removed from the deep layer, new trapped electrons are generated by the ultraviolet-rich erasing light itself.
In order to eliminate the above drawback, there has been developed a technology for applying first erasing light including a radiation in an ultraviolet wavelength range to a stimulable phosphor panel to remove trapped electrons from a deep layer region thereof and thereafter applying second erasing light in a wavelength range other than the ultraviolet wavelength range to remove trapped electron that have newly been generated in a relatively shallow layer by the first erasing light (see Japanese Laid-Open Patent Publication No. 5-119412). The technology increases the erasing efficiency by setting the first erasing light and the second erasing light to a certain light quantity ratio.
The distribution of trapped electrons in the stimulable phosphor panel depends on the dose of a radiation that is applied thereto. For example, if the dose of an applied radiation is low, then many trapped electrons are distributed in a surface layer of the stimulable phosphor panel, and if the dose of an applied radiation is high, trapped electrons are distributed also in a deep layer of the stimulable phosphor panel. Therefore, it is necessary to take into account the dose of the radiation applied to the stimulable phosphor panel in order to reliably erase the residual radiation image remaining in the stimulable phosphor panel.